Hi ebeck,
Pressure issues in the shoulders or hips (for side sleepers especially) are usually from a comfort layer that is too thin or firm and is often connected with some numbness or tingling in the limbs or joints or soreness on the pressure point. If you are experiencing pressure points then you probably need a little extra thickness/softness in the comfort layers.
If you are feeling lower back issues then this would take some detective work to identify the cause. For side sleepers it could be from layers that are too firm causing you to “twist” away from pressure causing alignment issues or it could be from comfort layers that are too thick and soft which allows the heavier parts of the body to sink in too far which can also cause alignment issues in the spine or joints if they are out of their neutral alignment for too long over the course of the night.
Stiffness is usually from muscles that aren’t able to fully relax over the course of the night either because the comfort layers aren’t soft enough and there is direct pressure on the muscles (like sleeping on the floor) or because the spine or joints are out of their neutral alignment and the muscles are “fighting” and tense over longer periods of time to maintain neutral alignment. Tis is like closing your hand in a tight fist and holding it there over a long period of time and then trying to open it again (the muscles will be stiff).
It can involve a little bit of detective work to decide what is the underlying cause of the symptoms you are experiencing.
Generally more specific descriptions of your “symptoms”, the parts of your body you are experiencing them, and the positions you tend to experience them along with your best judgement about whether they are pressure issues or alignment issues can be helpful in tracking down the cause of your symptoms
If I had to guess I would say that you may need a little extra softness / thickness in your mattress but of course this is only a guess because I can’t feel what you are feeling or see you on the mattress.
If you do need a topper and some extra softness/thickness in the comfort layers then post #8 here may be helpful as a guideline. Some careful and objective testing in the store (using the testing guidelines in post #1 here) comparing your mattress with others that are firmer or softer or on the same mattress you have with a topper on top of it (most stores that sell PLB also sell 2" and 3" latex toppers) may also be very useful if you listen carefully to the cues from your body.
Keep in mind that you are testing for PPP (Posture and alignment, Pressure relief, and Personal preferences) not just for subjective feelings of “showroom comfort” which may not translate very well into what you feel in the long term when you sleep on your mattress.
Phoenix